OK I've worked out how it was done.
What you do is this. You take one female victim, you take hold of her wrists, and force them above her head as you push her back against a wall. You can then use your arms to pin her arms against the wall, leaving both your hands free; one of which you can place on her mouth, and the other against her throat. If at the same time, you place your body at right angles to hers and thrust one knee between her legs, you can pin her lower body against the wall. She can then kick as much as she likes, but she can't make contact, and she can't move her arms, because you're using your entire body weight to pin them to the wall. And of course, all you need is 20 seconds worth of pressure to finish her off.
Now you're going to leave grip marks on her wrists, and it's possible, during the intitial struggle as you grapple with her wrists, that you might give her face a bash and give her a nose bleed, whilst she might well end up with other bruises and marks on her body, but most importantly she can't scratch or kick you, so she can't really injure or mark you. Which is a very good thing if you intend being seen in public soon afterwards. After you've popped home and changed naturally - you don't want to be seen with any blood on your shirt after all.
Now I've tried this and it works. OK, I left out the bloody nose bit. And the actual throttling to death bit as well, now that you come to mention it. There are limits to experimentation. But it does work, and it would appear to me to be a very effective method of homicide. However, I'm not sure how you'd come across it by accident.